Great strides have been made in understanding Listeria monocytogenes pathogenesis, especially at the cell biological level. One reason for this progress has been the extensive use of a single serogroup 1/2 L. monocytogenes strain, EGD. However, representative strains from other more prevalent serogroups, including serogroup 4, have remained understudied. Serogroup 4 strains constitute the preponderance of disease associated isolates from humans and other animals. Listerial serogroups are defined by their wall teichoic acid (WTA) structure. All listerial isolates have one of two fundamentally different WTA structures--those represented by the 1/2 serogroup structure and those represented by serogroup 4 structure. Recent independent studies indicate that certain alterations to serogroup 4 WTA composition are profoundly attenuating. In this proposal we examine the pathogenesis of a mouse oral virulent serogroup 4 strain. We have one specific aim: 1) Construct and characterize mutants that have altered serogroup 4 wall teichoic acid (WTA) composition. We will systematically alter the serogroup 4 WTA composition and correlate compositional changes to alterations in pathogenicity in vivo and in vitro. This aim has three objectives: (a) Mutant construction and biochemical characterization; allelic exchange will be employed to introduce in-frame deletion mutations into genes whose products are required for the generation of, and the proper substitution of the serogroup 4 WTA repeat unit. (b) Mutant characterization in vitro; intracellular growth and cell-to-cell spread will be assessed in cultured mouse enterocyte and macrophage monolayers. (c) Mutant characterization in vivo and ex vivo; the oral virulence of each mutant will be determined in infective index experiments that assess the degree of translocation of the mutants from the intestinal lumen. Additionally, the elicitation of inflammatory cell infiltrates, phagocytic killing by PMN and mononuclear phagocytes, and level of TNF production will be examined for each WTA mutant. Overall, we anticipate that our results will extend our knowledge of listerial pathogenesis in a highly relevant serogroup. Additionally, our results have the potential to impact national health policies and procedures in several areas. For example: (i) Risk assessment-a knowledge of how serogroup 4 WTA composition influences virulence could facilitate the development of simple lectin based assays to assess the need for product recalls in cases of listerial contamination. (ii) Diagnostics-a knowledge how WTA composition influences pathogenic potential and disease presentation could facilitate diagnosis, improve the specificity of diagnostic assays, and improve the power of epidemiological studies. (iii) Therapies--specific therapeutic strategies could expand treatment modalities (e.g., ones tailored to disrupt specific steps in WTA biosynthesis).